Users of mobile telephones or comparable mobile devices, such as smartphones, tablets or the like, use the device with a multiplicity of functions in all areas of daily life. The range of functions will continue to grow and create new possibilities for future generations of devices. More complex analysis aspects for assessing the quality of food and also in other areas, such as material analysis for detecting counterfeit products, all the way into the areas of fitness and health detection or even telemedicine, are expected to be a very important area.
Laboratory methods for a reliable analysis of organic objects, even including humans as a living system of organic material, are known and have become established. In recent years, a great deal of investment has been put into the miniaturization of the necessary components for mobile use. A highly promising approach is spectral analysis, in particular in the NIR spectral range, i.e. electromagnetic radiation in the wavelength interval from 780 nm to 2500 nm.
Documents WO 2003/069289 A1 and WO 2003/069290 A1 describe spectrometers that use a movable dispersive element, in particular, a rotating diffraction grating. The rotating diffraction grating is part of a monochromator, as a result of which the spectrometer requires only a single detector. The grating and its drive can be in the form of a microelectromechanical system (MEMS).
DE 10 2008 019 600 A1 discloses a MEMS hybrid spectrometer. Further miniaturization is achieved here by integrating a plurality of functional elements in the MEMS component. By way of the photolithography of the process technology, the grating and the slits can consequently be adjusted with a precision that is much more accurate than any manual component adjustment. The spectrometer is furthermore realized as a stack of substrates, with the result that it is possible in principle to build up a large number of systems to form a composite structure, to simplify adjustment, and to then singulate the systems.
A further miniaturized spectral analysis system is known from the document “Near-Infrared Grating Spectrometer for Mobile Phone Applications,” Applied Spectroscopy 70(5), 734-745 (2016) by T. Pügner, J. Knobbe, H. Grüger. The principle-based symmetry of the approach, wherein the grating always oscillates with equal amplitude from its rest position into both angular directions, makes it necessary to deviate from the classical approach of a Czerny-Turner spectrometer in the first order of diffraction, since otherwise the same spectral range for positive and negative deflection angles will be scanned twice. This problem has been solved by using the first negative order of diffraction. Here, the W-shaped beam path of a Czerny-Turner spectrometer is folded, and the entrance and exit slit are moved to the same side of the grating. However, use of the folded beam path is also associated with a problem. Instead of the spherical on-axis mirrors that are typical in a Czerny-Turner arrangement, off-axis bi-conic mirrors must be used for an acceptable imaging performance. These are complex to produce and are producible in volume only to a limited extent, or not in a sufficiently cost-effective manner, due to the currently available technologies.